Provided is a manufacturing method of a semiconductor element substrate including: a step of forming a first photoresist pattern on a first surface of a metallic plate, to form a semiconductor element mounting part, a semiconductor element electrode connection terminal, a wiring, an outer frame part, and a slit; a step of forming a second photoresist pattern on the second surface of the metallic plate; a step of forming the slit by half etching to connect the metallic chip with a four corners of the outer frame part; a step of forming a plurality of concaved parts on the second surface of the metallic plate; a step of forming a resin layer by injecting a resin to the plurality of concaved parts; and a step of etching the first surface of the metallic plate and forming the semiconductor element electrode connection terminal and the outer frame.